A dental prosthesis is fabricated by the application of a dental, ceramic opaque to a prosthetic substrate, usually platinum. The ceramic opaque is adapted to mask the dark color of the platinum substrate. Additionally, it forms an underlying layer which is adapted to receive an overlay of both a gingival and an incisal porcelain to form the finished dental prosthesis. While the gingival and incisal porcelains are of slightly different color as are the gingival and incisal enamels on a natural tooth, they are also somewhat translucent. Thus, it is essential that the underlying ceramic opaque completely mask the dark platinum substrate.
Presently, dental ceramic opaque is mixed with water to a light, workable consistency and painted upon the substrate. The water-based ceramic covers so poorly that usually several applications are necessary. However, when water is employed as the dispersant, subsequent applications erode and damage the underlying previous applications. Thus, it is frequently necessary to fire the ceramic opaque at high temperatures on the order of 1800.degree. F. before employing additional ceramic opaque. Each firing requires from 1.5 to 2.5 hours.
Gingival and incisal porcelain are also presently dispersed in water. Thus, it is absolutely necessary to fire the ceramic opaque after a satisfactory mask has been achieved, so that it will not dissolve, drift or otherwise be impaired under the influence of the water from the gingival and incisal porcelains.
Usually, the application of ceramic opaque to achieve a satisfactory mask requires 2 or 3 firings of 1.5 to 2.5 hours each resulting in a bisque sufficiently strong to receive water dispersed gingival and incisal porcelains. As a result, as much as 6.5 hours of firing time is consumed merely to achieve a proper mask of the platinum substrate by means of the ceramic opaque.
Thereafter, the gingival and incisal porcelains must be applied on top of the bisque of underlying ceramic opaque. The gingival and incisal porcelains are presently dispersed in water to a consistency which permits application to the ceramic opaque bisque. The water tends to evaporate rapidly with the porcelains returning to a powdery state which has very low mechanical strength. Therefore, it is extremely difficult to shape the tooth with the incisal and gingival porcelains because the working time is so short. Nevertheless, when the gingival and incisal porcelains are applied and shaped, the prosthesis is again fired until the gingival and incisal porcelains have fused. The fired prosthesis is now ready for finishing, carving and shaping by means of diamond stones and the like. After final shaping and fitting, a last firing is employed at somewhat higher temperatures than employed for the first firing so as to achieve a glazed surface.
Thus, in the current procedure, the prosthesis is fired four or five times, each firing requiring 1.5 to 2.5 hours. This is extremely tedious and time-consuming. Additionally, it is extremely difficult to shape the gingival and incisal porcelains when mixed with water by reason of their rapid drying and return to a powdery state.
It is among the objects and advantages of the present invention to provide a dispersant for the underlying ceramic opaque on dental prostheses and the like which will dry sufficiently rapidly under the relatively low temperatures of an infra red lamp to permit the addition of still more ceramic opaque, two, three, four or as many times as are necessary in order to insure complete masking of the substrate without resort to high temperature firing each time additional ceramic opaque is applied.
Another object of the invention is to provide a second dispersant for gingival and incisal porcelains which dries sufficiently rapidly under the relatively low temperatures of an infra red lamp so as to be easily carved without resort to high temperature firing thereby reducing high temperature, time consuming firings for the application of gingival and incisal porcelains to a single end firing for glazing.
Yet another object of the present invention is to provide first and second dispersants as aforesaid which are mutually compatible such that the ceramic opaque underlying layer need not be fired to a bisque prior to the application of gingival and incisal ceramic without danger of damage to the ceramic opaque mask over the substrate.
Still another object of the invention is to provide a dispersant for the application of ceramic opaque which is sufficiently resistant to water erosion when dried for a short time under an infra red lamp to accept water-based gingival and incisal porcelains without significant impairment.